1. Field of Invention
This invention relates to the field of data processing, and more particularly to a method for transferring data between electronic devices. The invention is especially adapted to testing systems comprising electronic devices, however, the invention is equally useful for transferring data into electronic devices under any condition.
2. Description of the Prior Art
Data processing systems typically consist of a central processing unit (CPU), RAM, ROM, and one or more input and output devices such as a keyboard and display. Great consumer interest has been generated in these system as their size has been reduced. The handheld personal calculator is but one example of the increased interest in small computing systems.
In order to reduce the size of these and similar systems, the industry has used increasing levels of integration to reduce both the size and number of integrated circuits employed in the system thereby combining many gates into a single integrated circuit and many integrated circuits into one or two integrated circuits. Today, the size of these integrated circuits is limited by the packaging and the need to get signals between each integrated circuit in the system. Each integrated circuit must have two power supply pins, one for the voltage supply line and one for the ground line. The definition of the remainder of the pins is determined by the designer. The selection of the definitions for the pins is a critical aspect in the design of any integrated circuit. For example, with a RAM or a ROM, unnecessary uses of pins can significantly reduce the amount of data that the RAM or ROM can access thereby driving up costs. Methods used to reduce the number of connection pins include multiplexing data and address busses and serializing the data to be transferred over the data and address busses.
Many modern consumer products are battery operated. Consumers usually prefer to be alerted that the batteries need replacement prior to the product failing rather than having for the power to fail during an important operation. Many modern consumer products monitor the voltage supply line and stop operation and notify the user when the batteries have passed their useful like. This is usually accomplished by making the system devices function properly with a wide variation in power supply voltage and then including a low power supply detection circuit which senses when the battery voltage has dropped below a particular level and then notifying the user accordingly.
Testing a device during its manufacture is necessary in order to provide reliable high quality products. However, testing the product does not necessarily enhance the marketability of a product, so it is not always desirable to dedicate a pin of an integrated circuit or program space in a ROM in order to test a product for manufacturing defects. Prior art solutions include mounting a test ROM in the test system fixture or programming the test system to intercept signals from the CPU for a particular address and then substitute the appropriate instructions from the test program. These test approaches require access to system status information or a very sophisticated expensive test system or both.